Prediction of Wave Impact in Extreme Weather

Abstract There is a need for improved analysis and verification tools against wave impact, partly due to updated metocean criteria in various geographical areas, but also due to the complex nature of the problem. Model tests are usually recommended in the final design verification. In this paper, improved engineering methods and procedures in predicting wave impact loads on FPSO's and offshore platforms in severe weather are described. Applications include wave-in-deck on jacket platforms, wave amplification with wave impact on large-volume platforms, green water /bow flare slamming on FPSO, and impact on columns. The resulting theoretical procedures and tools are in particular intended for early stages in the design. State-of-the-art knowledge is combined with systematic analyses of experimental data. New recommended tools and practical procedures for the fast, accurate and robust prediction of wave impact loads due to random waves are established and validated against model tests. Robust and practical methods are emphasized. Basic physical mechanisms and parameters critical to wave impact are pointed out. Experimental data includes existing data sets as well as new experiments. New engineering software tools are developed. Recommendations on model testing procedures are also given. Introduction Hydrodynamic impact loads resulting from random, extreme ocean waves are important factors in the design of ships and offshore structures. This includes extreme global loads such as ringing and whipping, global impact loads on fixed and floating platform type structures, and local impact loads due to green water, bow slamming and wave-in-deck impact forces. An example of the type of practical problems that may occur is the bow flare slamming event that was experienced on the Schiehallion FPSO North of Scotland /1/. The relevance of the wave impact problem is recently also increased due to new metocean criteria being established /2,3/. Because of the strongly nonlinear effects, and limited accuracy or robustness of available theoretical models for such applications, the loads are often estimated by use of model tests in offshore basins. Examples from experiments with structures in extreme waves are shown in Fig. 1.